There is a large amount of art relating to the production of sucrose polyols and other polyols produced with solid initiators. The process most commonly employed is described in U.S. Pat. No. 3,085,085 where sucrose is dissolved in water with an oxyalkylation catalyst such as potassium hydroxide. Alkylene oxide is added over a period of time until the reaction product is a liquid. At this stage the water is removed. The remaining alkylene oxide is then added until the desired polyether polyol is obtained. This method of making sucrose polyols has been found to be satisfactory for many purposes. However, the water present during the initial alkoxylation will react to some extent with the alkylene oxide to form bifunctional by-products. Because of the low equivalent weight of water, even small amounts of water reacting under these conditions will severely reduce the functionality of the resulting polyol. High functionality of sucrose polyols is required to enhance the dimensional stability of rigid polyurethane foams made with such polyols.
Severe problems arise when water cannot be used as a solvent for high melting sucrose. Normally, solid polyols such as sucrose undergo partial decomposition as they melt and these solid compounds are insoluble in any oxyalkylation-resistant solvents. Prior art in this regard is discussed e.g. in U.S. Pat. Nos. 3,190,927 and 3,346,557. In these patents a solution is given as to how to get sucrose into a form in which it can be alkoxylated. An adduct of the high melting polyol with 1 to 4 mols of an alkylene oxide is disclosed as a suitable solvent for the full alkoxylation process. The disadvantage of this process is that it must be carried out in two stages. A similar process is disclosed in U.S. Pat. No. 3,357,970.
In U.S. Pat. No. 3,442,888 the sucrose is mixed with a substantial amount of glycerol and an alkali metal hydroxide catalyst. These polyols, however, also suffer from the fact that glycerol, with a functionality of only three, must be used in large amounts. The products are inevitably low functional sucrose polyols.
In U.S. Pat. No. 3,640,997 sucrose is mixed with specific amounts of low functional ethylene diamine and a specific amount of an alkali metal hydroxide catalyst. The patent specifically discloses a lower limit of 0.6 mols of ethylene diamine which can be used per mol of sucrose. Less than this amount creates solubility problems. The sucrose cannot completely react and will precipitate out of the polyol. The use of at least 0.6 mols of ethylene diamine per mol of sucrose places an upper limit on the functionality of the polyol produced. The highest functional polyol in the examples of the patent is 5.6.
In U.S. Pat. No. 3,856,806 solid hydroxyl-containing initiators and a tertiary amine catalyst are directly alkoxylated with a blend of ethylene oxide and vicinal alkylene oxide having 3 to 4 carbon atoms. The process requires the blending of alkylene oxides.
In U.S. Pat. No. 3,941,769 sucrose is added to an inert aromatic hydrocarbon solvent such as toluene. Specific amounts of a short chain polyol, monoamine or polyamine, a small quantity of water, and a small amount of alkali metal hydroxide catalyst are added to the suspension followed by alkoxylation. High functional polyols can be produced by this method, i.e. with a functionality of 7 or more. However, polyols with a functionality of more than about 6.5 can only be obtained at the expense of cutting the alkoxylation short, i.e., stopping the alkoxylation before the OH number is reduced below about 400. Each polyol produced in the reference which has an OH number below 400 also has a functionality of significantly less than 6.5. Example 4 shows a polyol with a functionality of 7.18 but a hydroxyl number of 519 and viscosity of 400,000 cP. Polyols with viscosities in such a range cannot be easily handled by conventional foaming equipment. The viscosity can only be lowered as the alkoxylation proceeds and the OH number is lowered. The functionality of the resulting polyol would be significantly reduced as the alkoxylation continues because more and more water will react, forming difunctional polyols.
Most of the peculiar problems associated with making polyether polyols from solid initiators compounds containing hydroxyl groups stem from the fact that these compounds will not dissolve in typical solvents. The art has esssentially been led in the various directions mentioned above to circumvent this problem, a problem which is described in an early patent, U.S. Pat. No. 2,902,473 as follows--" . . . no practical solvent is known that will simultaneously dissolve these polyols, the alkylene oxides and the conventional caustic alkali catalysts without entering into reaction with the oxide" (column 1, lines 27-30).